Measurement of dielectric liquid level change in two-phase immersion cooling systems

ABSTRACT

The instant application pertains to new fluid level monitoring apparatus and a cooling system for computer components that employs the fluid level monitoring apparatus. In one embodiment, the liquid level measurement device comprises a load cell and a buoyancy element. The buoyancy element is configured to be partially submerged in the liquid phase. The load cell and the buoyancy element are operably connected such that a change in liquid volume may be determined using Archimedes&#39; principle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to PCT publication WO2020/102090 filed Nov.11, 2019 titled “Liquid Immersion Cooling Platform” owned by TMGCore,LLC which application is incorporated herein by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates to, for example, two-phase liquidimmersion cooling systems with a liquid level measurement and monitoringdevice.

BACKGROUND AND SUMMARY

Halocarbons such as perfluorocarbon liquid dielectric fluids such asNOVEC™ are frequently employed in immersion cooling of computercomponents such as servers. The fluid may be lost for various reasonssuch as when servers are swapped or due to leaks in the system. The lossof even small amounts of fluid can be both expensive and deleterious tothe system. Many common level sensors such as optical or ultrasonictypes may not be particularly effective when used with fluorocarbonliquids. Accordingly, what is needed are new methods and systems formeasuring the liquid level that are precise, efficient and/or effective.

Advantageously, the instant application pertains to new liquid levelmonitoring apparatus, methods, and systems. In one embodiment, theapplication pertains to a liquid level measurement device comprising aload cell and a buoyancy element. The buoyancy element is configured tobe partially submerged in the liquid phase. The load cell and thebuoyancy element are operably connected such that a change in liquidlevel may be determined using (1) the change in force measured by theload cell, (2) the density of the buoyancy element, (3) thecross-sectional area of the buoyancy element, (4) the density of theliquid, and (5) the movement of the buoyancy element due to the changein force on the load cell. That is, Archimedes' principle is employed.

In another embodiment the liquid level measurement device is employed inan immersion cooling system for computing components. In addition to themeasurement device, the system comprises a vessel configured to containa dielectric fluid in both liquid and vapor phases. A rack is configuredto hold one or more computer components such that one or more computercomponents are at least partially submerged within the liquid phase ofthe volume of thermally conductive, boilable, and condensable dielectricfluid. A condenser is configured for actively condensing a dielectricfluid from vapor phase to liquid phase.

These and other objects, features and advantages of the exemplaryembodiments of the present disclosure will become apparent upon readingthe following detailed description of the exemplary embodiments of thepresent disclosure, when taken in conjunction with the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present disclosure, together with furtherobjects and advantages, may best be understood by reference to thefollowing description taken in conjunction with the accompanyingdrawings.

FIG. 1 shows a representative liquid level measurement device.

FIG. 2 shows a representative of the overall method of calculatingvolume change using, for example, a liquid level measurement device ofthe present application.

FIG. 3 shows a view of a representative liquid level measurement devicelocated in a sump area of a cooling system vessel.

FIG. 4 shows a second view of a representative liquid level measurementdevice located in a sump area of a cooling system vessel.

DETAILED DESCRIPTION

The following description of embodiments provides non-limitingrepresentative examples to particularly describe features and teachingsof different aspects of the invention. The embodiments described shouldbe recognized as capable of implementation separately, or incombination, with other embodiments from the description of theembodiments. A person of ordinary skill in the art reviewing thedescription of embodiments should be able to learn and understand thedifferent described aspects of the invention. The description ofembodiments should facilitate understanding of the invention to such anextent that other implementations, not specifically covered but withinthe knowledge of a person of skill in the art having read thedescription of embodiments, would be understood to be consistent with anapplication of the invention.

In one embodiment the present application pertains to a liquid levelmeasurement device. While described herein as a component in animmersion cooling system for dielectric fluid, the liquid levelmeasurement device may be employed in virtually any environment withvirtually any liquid wherein precision, accuracy, or both are required.That is, an ordinarily skilled artisan would use the instant disclosureto modify materials and/or components of the liquid level measurementdevice to employ it in chemical reactors, water treatment facilities, orany other industrial, commercial, or household vessel where it isdesired to monitor fluid level.

The liquid level measurement device typically comprises a load cell anda buoyancy element. The type, capacity, size, and material of the loadcell may vary depending upon the application, the density and mass ofthe buoyancy element, density of the liquid, rate of liquid levelchange, magnitude of electrical and mechanical noises in theinstallation environment, compatibility of the fluid vapor with thevarious components of the load cell and/or other parameters. As usedherein “load cell” is any sensor for measuring force. Typical load cellsthat may be employed may include those that are mechanical, pneumatic,hydraulic, electric, or any combination of these. The load cell maydetect weight in any convenient manner such as using shear, bending,compression, or tension. Particularly useful load cells include straingauges with high precision.

A buoyancy element is employed which is usually configured to bepartially submerged in the liquid. Generally, the load cell and thebuoyancy element are operably connected such that a change in liquidlevel may be determined using (1) the change in force measured by theload cell, (2) the density of the buoyancy element, (3) thecross-sectional area of the buoyancy element, (4) the density of theliquid, and (5) the movement of the buoyancy element due to the changein force on the load cell.

The size, shape, and material of the buoyancy element may differdepending upon the properties of fluid being measured (such as density,surface tension, compatibility of fluid with the element), the vesselgeometry, environment conditions, mechanical noise level, magnitude ofexpected level change, ability to shed fluid from its surfaces, and thelevel measurement precision required. Materials such as metals, alloys,vitreous materials, various plastics, or combinations thereof may beemployed as the buoyancy element.

The load cell and the buoyancy element may be operably connected in anyconvenient manner so long as a change in level of the liquid may bedetermined. Useful configurations vary depending upon the specificbuoyancy element and the load cell employed. Generally, in oneembodiment the buoyancy element is configured to hang substantiallyvertically from the load cell such that the buoyancy element ispartially submerged in the liquid phase. The material for hanging may beany material that sufficiently holds the buoyancy element in the desiredposition and is compatible with the desired testing environment. Thus,in some embodiments the material may be somewhat flexible such a wire orstring-like material.

In some embodiments it may be desirable to employ an actuator, a motorsuch as a variable speed motor, or both. If employed either or bothwhich may be configured to facilitate raising and/or lowering thebuoyancy element. In this manner the amount of submersion of thebuoyancy element in the liquid may be precisely and/or accuratelycontrolled so that the buoyancy element may be positioned to optimizeanticipated level changes, which in turn leads to more precise and/oraccurate measurements of changes in level.

In some embodiments machinable metals like aluminum may be employed toobtain a precise cross-sectional shape. Thus, in some embodiments acylindrical or disk shaped buoyancy element may be employed that iscomprised of a metal such as aluminum. The size may vary and an aspectratio may be selected that corresponds to a desired sensitivity. In someembodiments, a disc shaped buoyancy element may have a diameter of fromabout 2, or from about 3, or from about 3.5 inches up to about 6, or upto about 5, or up to about 2.5 inches. In some embodiments, a discshaped buoyancy element may have a height of from about 0.5, or fromabout 0.75, up to about 1.5, or up to about 1 inch.

In some embodiments the liquid may be subject to some turbulence,motion, or other forces which could tend to disturb the measurements ofthe liquid level measurement device. In such cases it may be desirableto include a disturbance reducer. The form of such a disturbance reducermay vary depending upon the system and liquid being measured. In oneembodiment a housing which at least partially surrounds the buoyancyelement only, or the load cell and buoyancy element, may be employed.Such a housing is configured to reduce disturbances by reducing oreliminating interfering liquid movements other than gradual rising orfalling of the liquid level at or near the buoyancy element. The housingmay include features, such as one or more holes or slots, to allow freeingress and egress of liquid, to maintain the liquid level inside thehousing equal to the level outside the housing.

A processor may be employed and operably connected to the liquid levelmeasurement device if desired. Among other items, the processor may beconfigured to receive the force on the load cell and calculate thechange in liquid level using other known parameters such as the densityof the buoyancy element, the cross-sectional area of the buoyancyelement, and the density of the liquid. If desired, the processor may beconfigured to institute certain changes to the system based on thechange in liquid level. The processor may also be operably connected toother sensors such as a leak detector or fluid detector such that avariety of data may be processed and actions initiated, changed, orstopped. For example, depending upon the change in liquid levelmeasured, the processor may send a signal to add or remove liquid.

As described above, the liquid level measurement device may be used inmany different systems but is described herein as particularlyapplicable to a two-phase immersion cooling system for computingcomponents. The system may comprise a vessel configured to comprise avolume of thermally conductive, boilable and condensable dielectricfluid in a liquid phase and a vapor phase. A rack may be configured tohold one or more computer components such that the one or more computercomponents may be at least partially submerged within the liquid phaseof the volume of thermally conductive, boilable and condensabledielectric fluid. A condenser for actively condensing a vapor phasedielectric fluid to a liquid phase dielectric fluid is generallyemployed. The above-described liquid level measurement device may thenbe employed to determine a change in dielectric liquid volume. Ifdesired, the system may include a tank configured to comprise a volumeof thermally conductive, boilable and condensable dielectric fluid thatis separate from the vessel and contained within or exterior to thevessel. In this manner the system may be configured (1) to transferdielectric fluid from the tank to the vessel; or (2) to transferdielectric fluid from the vessel to the tank; or (3) both (1) and (2)based on the determined change in liquid volume.

The liquid level measurement device described above may be located atany convenient location within the vessel or the tank so long as changesin liquid level may be measured, and changes in liquid volume may bedetermined. The location may vary depending upon the system'sconfiguration and its components. In one embodiment, the vesselcomprises a bath area wherein the computer components are at leastpartially submerged. A sump area may be separated from the bath area bya weir such that the bath area maintains a relatively constant level offluid. Thus, in this configuration the liquid level measurement deviceis located in the sump area wherein fluid losses would result in areduction in the liquid level.

Generally, the methods of using the liquid level measurement device inthe two-phase immersion cooling system employ first operating the systemat a steady state. The buoyancy element is then positioned such that thedesired volume of the buoyancy element is submerged. The position mayvary depending upon the buoyancy element shape, overall system design,and anticipated level change, but in some embodiments such as thedisk-shaped element described above, at least about 20% and up to about80% of the volume of the buoyancy element may be submerged. In thismanner a change in liquid volume may be determined. Adjustments to thesystem may then be made depending upon a change in liquid volume.

FIG. 1 shows a representative liquid level measurement device comprisinga linear actuator with supporting brackets attached to a load cell whichis operably connected to the buoyancy element. A disturbance reducersuch as the stilling enclosure depicted is employed to minimize theeffect of liquid movements, other than the gradual rise or fall of theliquid level, on the force measurements.

FIG. 2 shows a representative method of calculating volume change using,for example, a liquid level measurement device such as that shown inFIG. 1. If desired, the method of FIG. 2 can be implemented with aprocessor connected to the liquid level measurement device. FIGS. 3 and4 show the liquid level measurement device within a representativetwo-phase immersion cooling system such as those described above. Asshown in FIGS. 3 and 4 the liquid level measurement device is locatedwithin a sump area of the vessel in the two-phase immersion coolingsystem. Such two-phase immersion cooling systems are described in moredetail in PCT publication WO2020/102090 filed Nov. 11, 2019 titled“Liquid Immersion Cooling Platform” and in U.S. Patent Publication20210022263 filed Sep. 14, 2020 titled “ABSORPTION/DESORPTION PROCESSESAND SYSTEMS FOR LIQUID IMMERSION COOLING.” Both applications are ownedby TMGCore, LLC and are incorporated herein by reference.

In some embodiments, the immersion cooling system can include a door.The door can provide access to the vessel and allow for removal andplacement of the computing components, e.g., by a robot. In someembodiments, a self-contained computing system may comprise a roboticsystem, such as, for example, a gantry robot, configured to remove,replace, and/or install blade servers, power supplies, or othercomponents, e.g., chassis. A self-contained system may comprise either a“robot on the inside” or a “robot on the outside” system. In someembodiments, the vessel, rack, computer components, power supplies,replacement magazine, and gantry robot may be arranged such that thegantry robot may remove, replace, and/or install components. It will beappreciated, that the gantry robot may be able to lift and lowercomponents in addition to traveling in a single linear direction.

Embodiments

1. A cooling system for computing components comprising:

a vessel configured to comprise a volume of thermally conductive,boilable and condensable dielectric fluid in a liquid phase and a vaporphase;

a rack configured to hold one or more computer components such that theone or more computer components may be at least partially submergedwithin the liquid phase of the volume of thermally conductive, boilableand condensable dielectric fluid;

a condenser for actively condensing a vapor phase dielectric fluid to aliquid phase dielectric fluid; and

a liquid level measurement device comprising a load cell and a buoyancyelement wherein the buoyancy element is configured to be partiallysubmerged in the liquid phase and wherein the load cell and the buoyancyelement are operably connected such that a change in liquid volume maybe determined.

2. The cooling system of embodiment 1 wherein the change in liquidvolume is calculated from (1) a change in force measured by the loadcell, (2) density of the buoyancy element, (3) cross-sectional area ofthe buoyancy element, (4) density of the liquid, and (5) movement of thebuoyancy element due to the change in force on the load cell.3. The cooling system of embodiment 1 wherein the buoyancy element isconfigured to hang substantially vertically from the load cell.4. The cooling system of embodiment 1 further comprising a tankconfigured to comprise a volume of thermally conductive, condensabledielectric fluid wherein the system is configured (1) to transferdielectric fluid from the tank to the vessel; or (2) to transferdielectric fluid from the vessel to the tank; or (3) both (1) and (2)based on a change in liquid volume.5. The cooling system of embodiment 1 further comprising an actuatorconfigured to raise and lower the buoyancy element.6. The cooling system of embodiment 1 further comprising a variablespeed motor configured to raise and lower the buoyancy element.7. The cooling system of embodiment 1 further comprising a housing whichat least partially surrounds the load cell and buoyancy element whereinsaid housing is configured to reduce disturbances.8. The cooling system of embodiment 1 wherein the vessel comprises asump area and a bath area and wherein the liquid level measurementdevice is located in the sump area.9. A liquid level measurement device comprising:a load cell; anda buoyancy element;wherein the buoyancy element is configured to be partially submerged ina liquid and wherein the load cell and the buoyancy element are operablyconnected such that a change in liquid volume may be determined.10. The liquid level measurement device of embodiment 9 wherein thechange in liquid volume is calculated from (1) a change in forcemeasured by the load cell, (2) density of the buoyancy element, (3)cross-sectional area of the buoyancy element, (4) density of the liquid,and (5) movement of the buoyancy element due to the change in force onthe load cell.11. The liquid level measurement device of embodiment 9 wherein thebuoyancy element is configured to hang substantially vertically from theload cell.12. The liquid level measurement device of embodiment 9 furthercomprising an actuator configured to raise and lower the buoyancyelement.13. The liquid level measurement device of embodiment 9 furthercomprising a variable speed motor configured to raise and lower thebuoyancy element.14. The liquid level measurement device of embodiment 9 furthercomprising a housing which at least partially surrounds the load celland buoyancy element wherein said housing is configured to reducedisturbances.15. The liquid level measurement device of embodiment 9 wherein theliquid level measurement device is configured to measure an amount ofdielectric liquid level change.16. The liquid level measurement device of embodiment 9 which furthercomprises a processor configured to receive the force in the load cell,and calculate the change in liquid volume.

In the preceding specification, various embodiments have been describedwith references to the accompanying drawings. It will, however, beevident that various modifications and changes may be made thereto, andadditional embodiments may be implemented, without departing from thebroader scope of the invention as set forth in the claims that follow.The specification and drawings are accordingly to be regarded as anillustrative rather than restrictive sense.

We claim:
 1. A cooling system for computing components comprising: avessel configured to comprise a volume of thermally conductive, boilableand condensable dielectric fluid in a liquid phase and a vapor phase; adoor; a sump area that is separated from a bath area of the vessel by aweir; a rack configured to hold one or more computer components suchthat the one or more computer components are configured to be: at leastpartially submerged within the liquid phase of the volume of thermallyconductive, boilable and condensable dielectric fluid; and lifted out ofthe volume of thermally conductive, boilable and condensable dielectricfluid when the door is open; a condenser for actively condensing a vaporphase dielectric fluid to a liquid phase dielectric fluid; and a liquidlevel measurement device comprising a load cell and a buoyancy elementwherein the buoyancy element is configured to be partially submerged inthe liquid phase and wherein the load cell and the buoyancy element areoperably connected such that a change in liquid volume may bedetermined.
 2. The cooling system of claim 1 wherein the change inliquid volume is calculated from (1) a change in force measured by theload cell, (2) density of the buoyancy element, (3) cross-sectional areaof the buoyancy element, (4) density of the fluid, and (5) movement ofthe buoyancy element due to the change in force on the load cell.
 3. Thecooling system of claim 1 wherein the buoyancy element is configured tohang substantially vertically from the load cell.
 4. The cooling systemof claim 1 further comprising a tank configured to comprise a volume ofthermally conductive, condensable dielectric fluid wherein the system isconfigured (1) to transfer dielectric fluid from the tank to the vessel;or (2) to transfer dielectric fluid from the vessel to the tank; or (3)both (1) and (2) based on a change in liquid volume.
 5. The coolingsystem of claim 1 further comprising an actuator configured to raise andlower the buoyancy element.
 6. The cooling system of claim 1 furthercomprising a variable speed motor configured to raise and lower thebuoyancy element.
 7. The cooling system of claim 1 further comprising ahousing which at least partially surrounds the load cell and thebuoyancy element wherein said housing is configured to reducedisturbances.
 8. The cooling system of claim 1, wherein the liquid levelmeasurement device is located within the sump area.
 9. The coolingsystem of claim 1, further comprising a housing which at least partiallysurrounds the load cell and the buoyancy element.
 10. The cooling systemof claim 9, further comprising an actuator configured to raise and lowerthe housing.
 11. A cooling system for computing components comprising: avessel configured to comprise a volume of thermally conductive, boilableand condensable dielectric fluid in a liquid phase and a vapor phase; asump area that is separated from a bath area of the vessel by a weir; arack configured to hold one or more computer components such that theone or more computer components are configured to be at least partiallysubmerged within the liquid phase of the volume of thermally conductive,boilable and condensable dielectric fluid; a condenser for activelycondensing a vapor phase dielectric fluid to a liquid phase dielectricfluid; and a liquid level measurement device comprising: a load cell; abuoyancy element; a housing which at least partially surrounds the loadcell and buoyancy element; and an actuator configured to raise and lowerthe housing; wherein the buoyancy element is configured to be partiallysubmerged in a liquid and wherein the load cell and the buoyancy elementare operably connected such that a change in liquid volume may bedetermined.
 12. The cooling system of claim 11 wherein the change inliquid volume is calculated from (1) a change in force measured by theload cell, (2) density of the buoyancy element, (3) cross-sectional areaof the buoyancy element, (4) density of the liquid, and (5) movement ofthe buoyancy element due to the change in force on the load cell. 13.The cooling system of claim 11 wherein the buoyancy element isconfigured to hang substantially vertically from the load cell.
 14. Thecooling system of claim 11 further comprising a variable speed motorconfigured to raise and lower the buoyancy element.
 15. The coolingsystem of claim 11 wherein the liquid level measurement device isconfigured to measure an amount of dielectric liquid level change. 16.The cooling system of claim 11 which further comprises a processorconfigured to receive a force in the load cell, and calculate the changein liquid volume.